Militants in Gaza fired rockets into a southern Israeli town on Tuesday during a visit by the UN Commissioner for Human Rights.

Witnesses said one person was critically wounded in the attack which hit a chicken slaughtering plant, just 200 metres from Commissioner Louise Arbour's convoy which was en route to the town of Sderot.

Arbour and members of a United Nations team, who are on a five-day trip to Israel and the Palestinian territories, were not hurt.

CTV's Janis Mackey Frayer was in Sderot when the warning sirens went off at about 8 a.m. local time.

"Within about 10 seconds we could hear the whoosh of the rocket and the impact," she told CTV.ca in an email.

"Arbour's convoy was coming into Sderot at the time -- she had spent the night in Gaza which obviously is very close. The rockets landed about 200 metres from the convoy, as it passed the industrial zone. She arrived at the mayor's office -- where we had been waiting -- and she was a bit shaken. Within a few minutes of meeting the mayor she asked if she could go and see the damage. So off we went."

But Arbour's team received an angry reception. Workers at the plant were clearly angry and shouted curses when Arbour insisted on seeing the result of Palestinian rocket fire firsthand.

Mackey Frayer said one worker began screaming and walking towards the convoy. The worker picked up some pebbles, one large rock and threw them toward the convoy before police restrained her.

"There is a real frustration among people there that this sort of thing happens almost every day and nobody -- not the government, not the UN, not the international community -- is doing anything about it," said Mackey Frayer.

Arbour has urged Israel to act in accordance with international law in the face of Palestinian militant attacks.

The former Canadian Supreme Court justice and chief prosecutor for UN war crimes tribunals said Israel "has a responsibility to defend its citizens, but has to do so only by legal means."

"It has to do so in line with international law, including international humanitarian law, but it has a primary responsibility to protect people who are under its authorities."

Anti-UN sentiment is running high in Sderot, which has been under missile fire from Palestinian militants in Gaza for three years.

The armed wing of Hamas claimed responsibility for the rocket attack.

The attack came on the day the Israeli military launched a three-pronged offensive in the northern Gaza Strip -- killing a top Hamas commander and an elderly Palestinian woman.

Israel intensified its military offensive against rocket-launchers in Gaza in recent weeks, in response to increased rocket attacks following Israel's weeklong incursion in the northern Gaza Strip town of Beit Hanoun earlier this month.

The operation on Tuesday began in the Zeitoun neighbourhood of Gaza City, then spread to the outskirts of Jebaliya and Beit Lahiya.

Witnesses told The Associated Press that ground troops, backed by helicopters, tanks and snipers, stormed the home of Ayman Hassanin, a local leader in the military wing of the ruling Hamas group.

Troops called on loudspeakers for Hassanin and his brother, Ibrahim, to surrender, according to the militants' mother. A fierce gunbattle followed, and Aymen Hassanin, 26, was killed, said Hamas.

Reports say violence in Gaza has been accompanied in recent months by increasing poverty brought on by international sanctions meant to force the Hamas-led government to recognize Israel and disarm.

Arbour said Tuesday's attack underlines the need for peace between Israel and the Palestinians.

She began her tour Monday in Beit Hanoun, where she met with families of 19 Palestinian civilians killed in Israeli artillery fire. Arbour angered Israeli officials by condemning Israeli military actions in the Gaza Strip, and told Palestinians that the world has not abandoned them.

Following the incident at the factory, Arbour continued her visit by visiting a daycare, where she sat with parents who talked of how their lives are impacted.

"In the middle of the discussion, the warning siren went off again," said Mackey Frayer. "People rushed to 'secure' rooms and we heard two more rockets land."

Arbour then went on to Abu Dis, a town famously divided down its main street by Israel's security barrier. She then moved on to Qalandiya checkpoint -- the main valve for the Palestinians who are allowed to travel to Jerusalem.

With reports from CTV's Middle East bureau chief Janis Mackey Frayer and The Associated Press